The present invention is directed, in general, to surface acoustic wave circuits and, more specifically, to a hermetic package for a surface acoustic wave circuit and method of manufacturing such hermetic package therefor.
Piezoelectric devices for use in electronic signal processing, especially surface acoustic wave (SAW) devices, have been advantageously adopted by the electronics industry. Such SAW devices have several advantages over more conventional technologies. For instance, they can be designed to provide complex signal processing in a single unit, and they also offer an additional benefit from their ability to be mass produced using semiconductor microfabrication techniques. These techniques lead to lower-cost devices having only small operating characteristic variations from unit to unit. Since SAW devices may be implemented in rugged, light-weight and power-efficient modules, they find many important applications, especially in mobile, wireless and spaceborne communication systems. Such communication systems typically operate over a wide range of frequencies from about 10 megahertz to about two gigahertz. The specific signal processing capabilities and frequency range of SAW devices may be determined to allow SAW devices to perform several roles in electronic systems.
An important feature of the SAW device is its geometry, which incorporates two metal patterns having interdigitated conductive lines or traces. Such interdigitated metal structures are formed on a piezoelectric substrate and act as input and output signal paths when an AC signal voltage is applied to one of the metal structures. This AC voltage induces a surface acoustic wave in the underlying substrate wherein the acoustic wave propagates to the output structure. The interdigitated metal lines of the signal receiving portion detect the acoustic wave and convert it into a filtered electrical output signal. SAW devices, operating in the Rayleigh wave mode, can generally be designed to provide bandpass filters that achieve responses that would otherwise require several hundred inductors and capacitors in conventional LC filter designs.
Proper operation and containment of the acoustic waves require precise construction. Existing surface acoustic wave device packaging has become well accepted in response to such requirements. Additionally, accurate and reliable performance of surface acoustic wave devices requires hermetic protection of the active surfaces of the devices. However, existing packaging practices often fail to fully and economically passivate the surface acoustic wave device active surface, thereby permitting particulate or contaminants to interfere with the active surface and render the performance of the SAW device inaccurate and unreliable. Such contamination concerns also exist with regard to other contact-sensitive electronic components, including other piezoelectric, pyroelectric and micro-electromechanical (MEMS) applications.
Accordingly, what is needed in the art is a hermetic package for surface acoustic wave devices and other contact-sensitive electronic components, as well as a method of manufacturing such a hermetic package.
To address the above-discussed deficiencies of the prior art, the present invention provides a SAW circuit package including: (1) a substantially planar piezoelectric substrate having an active surface, (2) an electronic circuit located over the active surface, (3) an encapsulant substrate having a bonding surface and (4) a bonding material interposing and creating a hermetic seal between the active surface and the bonding surface and around a void between the piezoelectric substrate and the encapsulant substrate. In one embodiment, the void has lateral dimensions at least equaling a footprint of the electronic circuit.
In one embodiment of the invention, the package further includes a passivation layer over the encapsulant substrate and spanning the encapsulant substrate and piezoelectric substrate. The passivation layer, while optional, may be desirable in certain applications.
In one embodiment of the invention, the encapsulant substrate comprises one selected from the group consisting of: (1) ceramic, (2) silicon and (3) glass.
In one embodiment of the invention, the piezoelectric substrate comprises one selected from the group consisting of: (1) bismuth germanium oxide, (2) gallium arsenide, (3) lithium borate, (4) lithium niobate, (5) langasite, (6) lithium tantalate, (7) lead zirconium tantalate (8) and quartz.
In one embodiment of the invention, the package further includes a plurality of vias containing metal, the metal contacting the electronic circuit to form terminals therefor. Those skilled in the pertinent art will recognize how such vias may be formed in the encapsulant substrate or, alternatively, in a passivation layer and/or the bonding material.
In one embodiment of the invention, the piezoelectric substrate and the encapsulant substrate have substantially coextensive footprints. Alternatively, the piezoelectric substrate may encompass the footprints of multiple encapsulant substrates.
In one embodiment of the invention, the electronic circuit comprises SAW circuit conductors that cooperate to form multiple SAW resonators. Those skilled in the pertinent art will recognize, however, that other applications may benefit from the architecture described herein, including hermetic wafer-scale and chip-scale packages for unpassivated piezoelectric, pyroelectric and MEMS devices.
In one embodiment of the invention, the void comprises a recess located on the bonding surface and/or the active surface.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.